In recent years there has been a greater need for clean energy as a measure against global warming, and use of thermoelectric effects is expected to increase. For example conversion of waste heat from thermal power stations, plants and automobiles to power using Seebeck effect elements has been proposed (see for example Patent Document 1).
However the current Seebeck effect elements are not sufficiently efficient, and it is necessary to increase the efficiency of thermoelectric conversion in order to put them into practice as a clean energy source.
The figure of merit Z—an indicator of the thermoelectric conversion efficiency—of conventional Seebeck effect elements using a dissimilar metal joint made of two metals having different Seebeck coefficients can be represented by the following formula (1) when S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity.Z=S2×(σ/κ)  (1)In addition, the electromotive force V is generated in a direction parallel to the temperature gradient ∇T.
In this case, the Seebeck coefficient S, the electrical conductivity σ and the thermal conductivity κ are all material parameters, and therefore the figure of merit Z also is a material parameter, and a thermoelectric conversion device having a high figure of merit Z is necessary in order to achieve thermoelectric power generation with high efficiency. Thus, it is necessary to develop a new material in order to increase the figure of merit Z.
Meanwhile, spintronics, which use the spin degree of freedom provided by electrons, as well as charge degree of freedom; that is to say, the spin angular momentum degree of freedom, have been drawing attention as a carrier for next generation electronics technology, which may substitute the charge degree of freedom of electrons used in conventional electronics, for example in semiconductor devices.
In spintronics the charge degree of freedom and spin degree of freedom of electrons are used simultaneously with the goal of finding new functions and properties. Most spintronic functions result when elements are driven by spin current.
Little spin angular momentum is dissipated in the spin current, and thus it is potentially usable for efficient energy transfer. Method for generating and detecting spin current are urgently needed.
Spin pumping has been proposed as one method for generating spin current (see for example Non-Patent Document 1). The present inventors have proposed a method for detecting spin current using the inverse spin-Hall effects.
The present inventors found out that a current flows in a direction perpendicular to the direction of the pure spin current when a pure spin current is injected into a sample, and that there is a difference in potential between the ends of the sample due to the inverse spin-Hall effects, and therefore it is possible to detect a pure spin current by detecting the difference in potential (see for example Non-Patent document 2).